Frontiers of Structural and Civil Engineering最新文献

In relation to the Shifu Road Station project on Line 4 of the Shenyang Metro in China, a small-pipe roof-beam method for constructing subway stations is presented. First, a numerical simulation was performed to optimize the supporting parameters of the proposed method and determine the design scheme. Subsequently, the deformation of the pipe roof and surface settlement during the construction process were investigated. Finally, the surface settlement attributed to the excavation was studied through field monitoring, and the proposed method was compared with other methods. The results show that an increase in the pipe-roof spacing has little effect on the surface settlement and pipe-roof deformation. The bearing capacity of the pipe roof can be efficiently utilized once the flexural stiffness reaches 2EI, and the flexural stiffness is not the dominant factor controlling the deformation. The essential stages in controlling surface settlement are the excavations of the transverse pilot tunnels and the soil between them. The final settlement value of the ground was 24.1 mm, resulting in a reduction in the construction period by at least five months while satisfying the control requirements.

Microbially induced carbonate precipitation (MICP) is a promising technique for the autonomous healing of concrete cracks. In this study, the effect of pH on MICP was investigated. The results indicate that the MICP process was inhibited when the pH was higher than 11. Both vaterite and calcite were produced when the pH was < 8, whereas only calcite was produced when the pH was > 8. Recycled concrete aggregates (RCA) coated with sodium silicate have been proposed as protective carriers for microbial healing agents. Although the presence of the coated RCA resulted in a loss of the splitting tension strength of the concrete, the loaded healing agents were highly efficient in self-healing cracks. Concrete incorporated with 20% RCA loaded with healing agents exhibited the best self-healing performance. When the initial crack widths were between 0.3 and 0.4 mm, the 7-d mean healing rate was approximately 90%. At 28 d, the crack area filling ratio was 86.4%, while its water tightness recovery ratio was 74.4% and 29.8%, respectively, for rapid and slow absorption. This study suggests that RCA coated with sodium silicate is an effective method for packaging microbial healing agents and has great potential for developing cost-effective self-healing concrete.

3D concrete printing has the potential to replace shotcrete for construction of linings of tunnels in hard rock. The shear strength of the interface between rock and printed concrete is vital, especially at super-early ages. However, traditional methods for testing the shear strength of the interface, e.g., the direct shear test, are time-consuming and result in a high variability for fast-hardening printed concrete. In this paper, a new fast bond shear test is proposed. Each test can be completed in 1 min, with another 2 min for preparing the next test. The influence of the matrix composition, the age of the printed matrices, and the interface roughness of the artificial rock substrate on the shear strength of the interface was experimentally studied. The tests were conducted at the age of the matrices at the 1st, the 4th, the 8th, the 16th, the 32nd, and the 64th min after its final setting. A dimensionless formula was established to calculate the shear strength, accounting for the age of the printed matrices, the interface roughness, and the shear failure modes. It was validated by comparing the calculated results and the experimental results of one group of samples.

The first exothermic peak of cement-based material occurs a few minutes after mixing, and the properties of three dimensional (3D) printed concrete, such as setting time, are very sensitive to this. Against this background, based on the classical Park cement exothermic model of hydration, we propose and construct a numerical model of the first exothermic peak, taking into account the proportions of C₃S, C₃A and quicklime in particular. The calculated parameters are calibrated by means of relevant published exothermic test data. It is found that this developed model offers a good simulation of the first exothermic peak of hydration for C₃S and C₃A proportions from 0 to 100% of cement clinker and reflects the effect of quicklime content at 8%–10%. The unique value of this research is provision of an important computational tool for applications that are sensitive to the first exothermic peak of hydration, such as 3D printing.

Segmental tunnel lining strengthened with steel plates is widely used worldwide to provide a permanent strengthening method. Most existing studies assume an ideal steel-concrete interface, ignoring discontinuous deformation characteristics, making it difficult to accurately analyze the strengthened structure’s failure mechanism. In this study, interfacial fracture mechanics of composite material was applied to the segmental tunnel lining strengthened with steel plates, and a numerical three-dimensional solid nonlinear model of the lining structure was established, combining the extended finite element method with a cohesive-zone model to account for the discontinuous deformation characteristics of the interface. The results accurately describe the crack propagation process, and are verified by full-scale testing. Next, dynamic simulations based on the calibrated model were conducted to analyze the sliding failure and cracking of the steel-concrete interface. Lastly, detailed location of the interface bonding failure are further verified by model test. The results show that, the cracking failure and bond failure of the interface are the decisive factors determining the instability and failure of the strengthened structure. The proposed numerical analysis is a major step forward in revealing the interface failure mechanism of strengthened composite material structures.

Single-layer reticulated shells (SLRSs) find widespread application in the roofs of crucial public structures, such as gymnasiums and exhibition center. In this paper, a new neural-network-based method for structural damage identification in SLRSs is proposed. First, a damage vector index, NDL, that is related only to the damage localization, is proposed for SLRSs, and a damage data set is constructed from NDL data. On the basis of visualization of the NDL damage data set, the structural damaged region locations are identified using convolutional neural networks (CNNs). By cross-dividing the damaged region locations and using parallel CNNs for each regional location, the damaged region locations can be quickly and efficiently identified and the undamaged region locations can be eliminated. Second, a damage vector index, DS, that is related to the damage location and damage degree, is proposed for SLRSs. Based on the damaged region identified previously, a fully connected neural network (FCNN) is constructed to identify the location and damage degree of members. The effectiveness and reliability of the proposed method are verified by considering a numerical case of a spherical SLRS. The calculation results showed that the proposed method can quickly eliminate candidate locations of potential damaged region locations and precisely determine the location and damage degree of members.

The simulation of fracture in large-scale structures made of porous media remains a challenging task. Current techniques either assume a homogeneous model, disregarding the microstructure characteristics, or adopt a micro-mechanical model, which incurs an intractable computational cost due to its complex stochastic geometry and physical properties, as well as its nonlinear and multiscale features. In this study, we propose a multiscale analysis-based dual-variable-horizon peridynamics (PD) model to efficiently simulate macroscopic structural fracture. The influence of microstructures in porous media on macroscopic structural failure is represented by two PD parameters: the equivalent critical stretch and micro-modulus. The equivalent critical stretch is calculated using the microscale PD model, while the equivalent micro-modulus is obtained through the homogenization method and energy density equivalence between classical continuum mechanics and PD models. Numerical examples of porous media with various microstructures demonstrate the validity, accuracy, and efficiency of the proposed method.

The pipe roofing method is widely used in tunnel construction because it can realize a flexible section shape and a large section area of the tunnel, especially under good ground conditions. However, the pipe roofing method has rarely been applied in soft ground, where the prediction and control of the ground settlement play important roles. This study proposes a sliced-soil–beam (SSB) model to predict the settlement of ground due to tunnelling using the pipe roofing method in soft ground. The model comprises a sliced-soil module based on the virtual work principle and a beam module based on structural mechanics. As part of this work, the Peck formula was modified for a square-section tunnel and adopted to construct a deformation mechanism of soft ground. The pipe roofing system was simplified to a three-dimensional Winkler beam to consider the interaction between the soil and pipe roofing. The model was verified in a case study conducted in Shanghai, China, in which it provided the efficient and accurate prediction of settlement. Finally, the parameters affecting the ground settlement were analyzed. It was clarified that the stiffness of the excavated soil and the steel support are the key factors in reducing ground settlement.

The slab of the composite girder is usually very wide in composite cable-stayed bridges, and the main girder has an obvious shear lag. There is an axial force in the main girder due to cable forces, which changes the normal stress distribution of the composite girder and affects the shear lag. To investigate the shear lag in the twin I-shaped composite girder (TICG) of cable-stayed bridges, analytical solutions of TICGs under bending moment and axial force were derived by introducing the additional deflection into the longitudinal displacement function. A shear lag coefficient calculation method of the TICG based on additional deflection was proposed. Experiments with three load cases were conducted to simulate the main girder in cable-stayed bridges. And the stress, deflection, and shear lag coefficient obtained from the theoretical method considering additional deflection (TMAD) were verified by the experimental and finite element results. A generalized verification of a composite girder from existing references was made, indicating that the proposed method could provide more accurate results for the shear lag effect.

Previous research has shown that using buckling-restrained braces (BRBs) at hinged wall (HW) base (HWBB) can effectively mitigate lateral deformation of steel moment-resisting frames (MRFs) in earthquakes. Force-based and displacement-based design methods have been proposed to design HWBB to strengthen steel MRF and this paper comprehensively compares these two design methods, in terms of design steps, advantages/disadvantages, and structure responses. In addition, this paper investigates the building height below which the HW seismic moment demand can be properly controlled. First, 3-story, 9-story, and 20-story steel MRFs in the SAC project are used as benchmark steel MRFs. Secondly, HWs and HWBBs are designed to strengthen the benchmark steel MRFs using force-based and displacement-based methods, called HWFs and HWBBFs, respectively. Thirdly, nonlinear time history analyses are conducted to compare the structural responses of the MRFs, HWBBFs and HWFs in earthquakes. The results show the following. 1) HW seismic force demands increase as structural height increases, which may lead to uneconomical HW design. The HW seismic moment demand can be properly controlled when the building is lower than nine stories. 2) The displacement-based design method is recommended due to the benefit of identifying unfeasible component dimensions during the design process, as well as better achieving the design target displacement.